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Researchers at the Naval Research Laboratory claim to have come up with a better tool for underwater acoustics. The new system uses laser light to create sound underwater from a distance. This technology could allow planes a much easier method of communicating with submarines without the need for a floating buoy. "Efficient conversion of light into sound can be achieved by concentrating the light sufficiently to ionize a small amount of water, which then absorbs laser energy and superheats. The result is a small explosion of steam, which can generate a 220 decibel pulse of sound. Optical properties of water can be manipulated with very intense laser light to act like a focusing lens, allowing nonlinear self-focusing (NSF) to take place. In addition, the slightly different colors of the laser, which travel at different speeds in water due to group velocity dispersion (GVD), can be arranged so that the pulse also compresses in time as it travels through water, further concentrating the light. By using a combination of GVD and NSF, controlled underwater compression of optical pulses can be attained."

Giving your position away to everyone when wants to know sometimes feels like it's been a mainstay of the US submarine service since the 60s, If they really give a damn that their subs will be even noisier when everyone else is working on making them as stealthy as possible, they'd probably build a few non-nukes.

220 decibels of sound can travel very far (especially underwater), I bet the submarine can be quite far away and will still be able to pick up the sound signal. IF (and this 'if' is a very handwavey kind of if) the range of this is say more than a few tens of kilometers, it would be hard to find the submarine anyway in a volume that large.

Based on the article, being able to generated phased sound at multiple points would be an improvement over the current method of dunking a speaker in the water. This would have the ability to transmit from mulitple points and create a directional sound, in theory pointed away from the enemy and towards the friendly.

Part of the general Internet phenom, "I just read the headline of an article, and my first thought will be a brilliant insight that people who devote their lives to this subject won't have thought of."
Elivated to an art form in left-wing critiques of millitary affairs, and right-wing attacks on evolution and climate science.

That's sort of like hiding the rubber ball under an infinite number of cups. The problem is the enemy can track every single cup. Humans are terrible about coming up with truly random patterns so eventually some sort of pattern would show up in the tracking and predictive analysis would start to give the enemy an idea of where to look.

It would also be expensive in fuel, wear and tear, and the occasional loss of crew and aircraft to keep a pseudo random lasercomms program running. We don't even patrol fo

You think they can build a global sensor net and detect every time the laser is used?

I think it would be enough for computers onboard a plane that has a message to send to periodically activate the laser to send the (timestamped, encrypted) message at random intervals during the flight.

Enemies in the water that receive the signal will have no idea as to the ultimate destination of the aircraft, only presumably that the sub may have been expected to be (at

So what's to prevent someone's hydrophones from picking this up and realizing that there's a submarine within audible range of the communication?

maybe the fact that it will not be used from the submarine platform. The navy has been investigating the use of blue-green lasers [navysbir.com] for one way comms to submarines for ages, both to improve bandwidth and to reduce the footprint of the signal. I do not see this as a communication tool, in my view it's an high tech Sonar Ping generator. [soundsnap.com] with enough computing power and using part of the bandwidth to signal the precise location of the laser hits, it might turn into a bistatic active sonar, in which the a

Dropping a sonobuoy and transmitting a message tends to have the same effect.

There are apparently circumstances when you need to have a chat with a submarine and it's worth giving away that there's a sub somewhere within X km, in some direction. On the other hand, since you don't have to drop a buoy every time, with the laser system you could potentially go around broadcasting some dummy messages too.

Also, letting people know that there's a sub somewhere within X km (where x is a fairly large number, the sub could hear a 200+ dB signal for a long way) is less useful than you might think. A circle several kilometers in radius is still a pretty big place to look for a sub, if you even happen to have a platform within range that could do the searching.

So it seems this would be a great excuse to put a reasonably high powered laser in space.

It could communicate with submarines over a vast area (I don't mean by illuminating the entire area at once, instead it would target many different pinpoint locations only one of which has the submarine it wants to communicate with).

The enemy wouldn't even be able to follow the track of aircraft that would otherwise be communicating with the submarines.

To Swimmers and wildlife, when a plane is shooting this giant high-powered laser into the water, to communicate with the submarine?

achieved by concentrating the light sufficiently to ionize a small amount of water, which then absorbs laser energy and superheats. The result is a small explosion of steam, which can generate a 220 decibel pulse of sound.

It would pose a danger if you were in the area. However, submarines aren't usually found in surfer territory and anybody swimming in the North Atlantic is probably glad to see the plane.
As for marine life, you can make the sound of a high enough frequency that marine life will be unaware and unaffected. It's not like we'll be using this as a bitchin' megaphone for unencrypted voice.

I don't know how the audio volume of this system compares with sonar systems (though the article's 220db and 160db from http://www.oceanmammalinst.org/mgpaper.html kind of gives clues and weakly suggest might be as much as 64x), but I suspect the people who oppose the use of sonar by the navy on the theory that it hurts whales are going to go nuts over this one.

There is no where near enough info to actually assess any kind of threat, but I'm sure the panic button will be hit anyway.

Active Sonar output is limited by cavitation. That is the boiling of the water on the surface of the transducer, which acts like a blanket attenuating and distorting the output. In general that means under 200 dB. Still plenty to cause problems with local wildlife. Active sonar is not used very often at its also like turning on a spotlight in a dark room.

The 220 db figure is probably the sound pressure right at the surface of the bubble. That tells you nothing useful as to the hazard to wildlife: depending on the pulse energy and repetition rate the bubbles could be as small as a few microns in diameter and the sound level nearby quite modest. The ability to create large "virtual" phased arrays should also reduce the need for the very high energy pulses used in some current systems.

I hope it does push the panic button.
It is one thing for us to defend ourselves. It is quite another for us to make another species miserable or extinct while attempting to optimize a way to defend ourselves from our own fears. Public outcry and discussion can give us pause so that we can investigate whether the effectiveness outweighs the possible ethical costs, and hopefully come up with a thoughtful solution.

Let's play devil's advocate and assume the Navy is needed and capable of "defending ourselves."How many whales are worth one human life? How much whale misery is equal to human misery? What are the ethics of letting humans (of any nation) die in order to save a whale or give said whale a better life?

I ask this simply because you put it in the context of defense, not (financial) cost.

This is the one environmental question I don't see asked enough. Choosing the less effective method for environmenta

Get back to me when there are 6 billion whales with and expected increase of 3 billion over the next decade or so. I would be willing to give up a nation of people if I could put the ocean back the way it was a hundred years ago.

Intro to moral philosophy was not my best class. But a lottery would certainly be fair. Instead I would suggest we outlaw those activities that cause harm, let's not argue about the method of measurement, to the ocean, or specifically whales. And if in fact as some ancestor post suggested this will result in human death, then so be it. You know, it is demonstrable that lowering the speed limit on highways reduces death by collision, but we re perfectly happy to leave the limit high for our convenience. Seem

I wonder how many marine animals we'll cause to go deaf from this, which would probably end any chance of survival for those affected. http://www.makeitlouder.com/Decibel%20Level%20Chart.txt 220 decibels is incredibly loud in the air, I can only guess the extended intensity it travel with underwater...

You are mixing up apples and oranges. The dB level in the water is not directly related to the dB level in the air. As Discovery of Sound in the Sea [dosits.org] says:

Confusion arises because relative sound intensities given in dB in water are not directly comparable to relative sound intensities given in dB in air.

...
The result is that sound waves with the same intensities in water and air when measured in watts per square meter have relative intensities that differ by 61.5 dB. This amount must be subtracted from relative intensities in water referenced to 1 microPascal (ÂPa) to obtain the relative intensities of sound waves in air referenced to 20 microPascals (ÂPa) that have the same absolute intensity in watts per square meter.

Dolphins and Orcas already casted their veto, but we will probably see more of their beaching suicide attempts to flash their opinion on the matter in the near future. Maybe those stupid humans would finally get any clue.

Potential injury to marine life aside - I'm interested to know how such a system can overcome the extreme variability of seawater. From what I just read this isn't as simple as sonar sending a circular pulse out and getting a 'bounceback'; this is sending information. Surely the abundance of microorganisms, animal matter, let alone local variations in saline and other chemical content which strongly define the physical properties of seawater would be difficult to adjust for?